Space communications using a geostationary satellite, including transmissions of such as high quality TV signals, still image signals, PCM audio signals and/or facsimile signals, are beginning to be put into practical use in many countries of the world (see I.E.E. Conf. Publ., (219), 365-368 (1983) and Conf. Ree. Int. Conf. Commun., Vol. 1/2, 26.1.1-26.1.5 (1981)). However, with a large number of such geostationary satellites in the single orbit, there is a significant signal interference thereamong. In order to reduce such interference, it may be helpful to provide to a receiving antenna a channel discrimitation function utilizing the cross polarization if linear polarization is employed. That is, it may be enough to match a plane of polarization of the antenna to a plane of horizontal or vertical polarization from the satellite. However, it is difficult to match the polarization planes to each other, due, for example, to deviations of the plane of polarization from the satellite by ionspheric disturbance and/or of the propagation path and the incident angle of the wave at the receiving site.
However, if a circular polarization is used for the satellite communication, the channel discrimination can be easily achieved by merely directing an antenna to a desired satellite correctly. Such adjustment of the direction of the receiving antenna is very easy compared with the case of the linear polarization.
For this reason, in future satellite communication systems, the circular polarization is expected to be generally used. Conventionally used circular polarization antennas include those of a conical horn type, a dipole type comprising two dipoles combined together orthogonally, and a parabola type using any of the above type antenna as a primary radiator.
In general, the parabolic antenna is made of a metallic plate or metallic net. Since, however, the metal is subjected to corrosion, it is necessary to use anticorrosive alloys or to apply anticorrosive coating. These anticorrosive alloys, however, are expensive. In the case of applying an anticorrosive coating, it is necessary to apply repeated coatings in order to provide satisfactory anticorrosion properties. This results in high production costs. Furthermore, if such an antenna is used for long periods of time, the coating is deteriorated. An attempt has been made to produce a wavereflecting plate comprising a thermoplastic resin (e.g., an unsaturated polyester resin) layer and a glass fiber layer, the surface of which has been metallized as a wave-reflecting layer (see U.S. Pat. Nos. 4,188,358 and 3,536,800). This is complicated in a method of production and, furthermore, it is very difficult to produce a wave-reflecting layer having a uniform thickness, i.e., having no irregularity in thickness.